Oxide composite particle and method for its production, phosphor and method for its production, color filter and method for its manufacture, and color display

ABSTRACT

An oxide composite particle of the present invention is composed of at least one fine gold particle contained in a matrix of an oxide particle or at least one fine gold particle supported fixedly on the surface of an oxide particle, and absorbs a visible light having a specific wavelength. A phosphor of the invention has a thin film which is composed of such oxide composite particles on the surface of a phosphor particle of red or the like. The phosphor can be obtained by mixing phosphor particles into a dispersion of gold colloid/oxide composite particles, agitating the resultant mixture, and taking out the precipitated phosphor particles, followed by drying. Further, in a color filter of the invention, a filter layer of at least one color formed on an inner surface of a panel is a thin film composed of the above-described oxide composite particles. This provides a phosphor or color filter which is excellent in optical characteristics, heat resistance and non-toxicity and never interferes with the irradiation of a photoresist with ultraviolet rays, and realizes a color display which exhibits good luminous chromaticity and is excellent in brightness and contrast.

This application is a 371 application of PCT/JP01/02975, filed Apr. 06,2001.

TECHNICAL FIELD

The present invention relates to an oxide composite particle usable as apigment which is excellent in heat resistance and light resistance andhas a high color purity, and a method for its production, a phosphor anda method for its production, a color filter and a method for itsmanufacture, color displays such as a color cathode ray tube, a fieldemission display (FED), a plasma display panel (PDP) and the likeincluding the above.

BACKGROUND

Generally, phosphor layers of blue, green and red are arranged in theshape of dots or stripes on an inner surface of a face panel of a colordisplay such as a color cathode ray tube, and electron beams collidewith the phosphor layers to cause their phosphors to emit light inrespective colors, thereby displaying an image.

Conventionally, for the purpose of improving the brightness, contrastand luminous chromaticity of such a color display, there has beenemployed a method of coating the surface of a phosphor particle withpigment particles of each color which transmit light of the same coloras its luminous color, or a method of providing, between a phosphorlayer and a face panel, a color filter composed of a pigment layer ofeach color which transmits light of the same color as the luminous colorof the phosphor layer.

It is possible to use an organic or inorganic pigment as a phosphorcoating or color filter forming pigment, but there is a limit in usablepigments because of their optical characteristics, heat resistance ortoxicity. More specifically, organic pigments, which are excellent inoptical characteristics but inferior in heat resistance, cannot be usedfor color displays including a cathode ray tube which require a heattreatment step. Further, cadmium pigments of the inorganic pigmentsexhibit good optical characteristics and heat resistance but cannot beused because of its toxicity.

Therefore, as a red pigment for a phosphor coating or color filter of acolor display, red iron oxide (Fe₂O₃), which is excellent in heatresistance and nontoxic, has to be used though it is somewhat inferiorin optical characteristics.

However, since red iron oxide has optical characteristics of greatlyabsorbing wavelengths within the ultraviolet region, the light exposureto a photoresist is decreased in a step of forming a phosphor layer andthe like when the surface of a phosphor is coated therewith or a colorfilter is formed therewith. In other words, in the formation of aphosphor layer by the photolithography, the phosphor coating film or thecolor filter containing red iron oxide absorbs a part of ultravioletrays which are applied to cure a photoresist, thus presenting a problemthat the photoresist is not sufficiently irradiated with ultravioletrays.

Accordingly, a phosphor coating and color filter material is demandedwhich is excellent in optical characteristics, heat resistance, andnon-toxicity, and never interferes with the irradiation of a photoresistwith ultraviolet rays in forming a phosphor layer and the like.

The present invention is made to solve these problems and it is anobject of the invention is to provide a phosphor or color filter whichis excellent in optical characteristics, heat resistance andnon-toxicity, and never interferes with the irradiation of a photoresistwith ultraviolet rays in forming a phosphor layer and the like.

Further, it is another object of the invention to provide a colordisplay which includes the phosphor or color filter and exhibits goodluminous chromaticity and excellent display characteristics such asbrightness and contrast.

SUMMARY

A first aspect of the present invention is an oxide composite particlecomprising an oxide particle matrix and at least one fine gold particlecontained in the oxide particle matrix, wherein a visible light having aspecific wavelength is absorbed.

A second aspect of the present invention is an oxide composite particlecomprising an oxide particle and at least one fine gold particle fixedon a surface of the oxide particle, wherein a visible light having aspecific wavelength is absorbed.

A third aspect of the present invention is a method for producing anoxide composite particle comprising preparing an aqueous dispersion offine gold particles, adding a surface-active agent and a hydrophobicorganic solvent to the aqueous dispersion of the fine gold particlesobtained in the previous step to form reverse micelles of the fine goldparticles, and adding tetraethoxysilane to the reverse micelles of thefine gold particles formed in the previous step for polymerization.

A fourth aspect of the present invention is a phosphor disposed to forma layer on an inner surface of a panel of a color display, comprising athin film containing the oxide composite particle as set forth in thefirst aspect on a surface of a phosphor particle.

A fifth aspect of the present invention is a phosphor disposed to form alayer on an inner surface of a panel of a color display, comprising athin film containing the oxide composite particle as set forth in thesecond aspect on a surface of a phosphor particle.

A sixth aspect of the present invention is a method for producing aphosphors comprising adding an organic or inorgapic binder to asuspension of a phosphor to allow the binder to adhere to a surface of aparticle of the phosphor, and thereafter adding a dispersion containingthe oxide composite particle as set forth in the first aspect theretoand mixing followed by drying to form a thin film containing the oxidecomposite particle on the surface of the phosphor particle.

A seventh aspect of the present invention is a method for producing aphosphor comprising adding an organic or inorganic binder to asuspension of a phosphor to allow the binder to adhere to a surface of aparticle of the phosphor, and thereafter adding a dispersion containingthe oxide composite particle as set forth in the second aspect theretoand mixing followed by drying to form a thin film containing the oxidecomposite particle on the surface of the phosphor particle.

An eighth aspect of the present invention is a color filter comprisingfilter layers of a plurality of colors arranged in a predeterminedpattern on an inner surface of a panel having a light transmissionproperty, characterized in that the filter layer of at least one coloris a thin film containing the oxide composite particle as set forth inthe first aspect.

A ninth aspect of the present invention is a color filter comprisingfilter layers of a plurality of colors arranged in a predeterminedpattern on an inner surface of a panel having a light transmissionproperty, characterized in that the filter layer of at least one coloris a thin film containing the oxide composite particle as set forth inthe second aspect.

A tenth aspect of the present invention is a method for manufacturing acolor filter comprising adding an organic or inorganic binder to adispersion containing the oxide composite particle as set forth in thefirst aspect, thereafter applying a resultant solution onto a panelhaving a light transmission property followed by drying to form a thinfilm containing the oxide composite particle.

An eleventh aspect of the present invention is a method formanufacturing a color filter comprising adding an organic or inorganicbinder to a dispersion containing the oxide composite particle as setforth in the second aspect, and thereafter applying a resultant solutiononto a panel having a light transmission property followed by drying toform a thin film containing the oxide composite particle.

A twelfth aspect of the present invention is a color display comprisinga panel having a light transmission property, a light absorbing layerdisposed on an inner surface of the panel and a phosphor layer disposedon a rear side opposite to the panel with respect to the light absorbinglayer, wherein the phosphor layer includes the phosphor as set forth inthe fourth aspect.

A thirteenth aspect of the present invention is a color displaycomprising a panel having a light transmission property, a lightabsorbing layer disposed on an inner surface of the panel and a phosphorlayer disposed on a rear side opposite to the panel with respect to thelight absorbing layer, wherein the phosphor layer includes the phosphoras set forth in the fifth aspect.

A fourteenth aspect of the present invention is a color displaycomprising a panel having a light transmission property, a lightabsorbing layer and a color filter respectively disposed on an innersurface of the panel, and a phosphor layer disposed on a rear sideopposite to the panel with respect to the color filter, wherein thecolor filter is the color filter as set forth in the eighth aspect.

A fifteenth aspect of the present invention is a color displaycomprising a panel having a light transmission property, a lightabsorbing layer and a color filter respectively disposed on an innersurface of the panel, and a phosphor layer disposed on a rear sideopposite to the panel with respect to the color filter, wherein thecolor filter is the color filter as set forth in the ninth aspect.

In the oxide composite particle of the first aspect of the presentinvention, at least one fine gold particle is contained in a matrix ofan oxide particle, and in the oxide composite particle of the secondaspect of the present invention, at least one fine gold particle isfixed on the surface of an oxide particle. In either aspect, since avisible light of a specific wavelength is absorbed, a phosphor can beobtained which is excellent in optical characteristics, heat resistanceand non-toxicity by coating the surface of a phosphor particle with theoxide composite particles. Further, the surface of a substrate such as aglass panel is coated with the oxide composite particles to form a thinfilm, so that a color filter which is excellent in opticalcharacteristics, heat resistance, non-toxicity and the like, can beobtained.

In a thin film singly composed of fine gold particles, the particlesaggregate together due to drying or grow to be black. But, the fine goldparticle is kept fine in particle diameter without turning to blacksince the fine gold particles are uniformly dispersed in a thin filmcomposed of the oxide composite particles, so that visible light is keptselectively absorbed.

Further, in the phosphor coated with the oxide composite particles ofthe present invention and the color filter formed of the oxide compositeparticles, since the oxide composite particle has opticalcharacteristics that its absorption of light within the ultravioletregion is significantly lower than that of red iron oxide which has beenconventionally used as a red pigment, ultraviolet irradiation of aphotoresist is never interfered with in forming a phosphor layer and thelike, so that the photoresist can be irradiated with a sufficient amountof ultraviolet rays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of a goldcolloid/oxide composite particle that is a first embodiment of thepresent invention.

FIG. 2 is a graph representing the zeta potential of the gold colloid.

FIG. 3 is a cross-sectional view showing the structure of a golfcolloid/oxide support particle that is a second embodiment of thepresent invention.

FIG. 4 is a cross-sectional view generally showing the configuration ofa phosphor with a surface covered with a coating film composed of a goldcolloid/oxide composite particle, which is a third embodiment of thepresent invention.

FIG. 5 is a cross-sectional view generally showing the configuration ofa color filter for a cathode ray tube, which is a fourth embodiment ofthe present invention.

FIGS. 6A and 6B showing a color cathode ray tube that is a first exampleof a color display of the present invention, FIG. 6A is across-sectional view generally showing the entire configuration, andFIG. 6B is an enlarged cross-sectional view of a phosphor screen.

FIG. 7 is a cross-sectional view generally showing the configuration ofan FED that is a second example of a color display of the presentinvention.

FIG. 8 is a cross-sectional view generally showing a PDP that is a thirdexample of a color display of the present invention.

FIG. 9 is a graph presenting the relationship between the particlediameter of the gold colloid and optical characteristics (the wavelengthhaving the maximum absorption) of a thin film composed of a goldcolloid/silica composite particle in the present invention.

FIG. 10 is a graph presenting the relationship between the particlediameter of the gold colloid and chromaticity characteristics of redluminescence in a color display of the present invention.

FIG. 11 is a chart presenting the transmittance spectrum of a thin filmcomposed of the gold colloid/silica composite particles and a filterlayer formed using red iron oxide.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, preferred embodiments of the present invention will beexplained. It should be noted that the invention is not limited to thefollowing embodiments.

FIG. 1 is a cross-sectional view of an oxide composite particle that isa first embodiment of the invention. This oxide composite particle has astructure in which at least one fine gold particle (gold colloid) 2 iscontained in a matrix of an oxide particle 1. Hereafter, a particlehaving such a structure is referred to as a gold colloid/oxide compositeparticle.

The diameter of the fine gold particle 2 preferably ranges from 2.5 nmto 35.0 nm. The particle diameter more preferably ranges from 10.0 nm to30.0 nm, and the most preferably from 10.0 nm to 25.0 nm.

As the oxide constituting the matrix in which the fine gold particle 2is contained, an oxide transparent to visible light is used. Suchpossible transparent oxides include silica (SiO₂), aluminum oxide(Al₂O₃), cerium oxide (Ce₂O₃), indium oxide (In₂O₃), lanthanum oxide(La₂O₃), tin oxide (Sno₂), tantalum oxide (TaO_(x)), zinc oxide (ZnO₂),titanium oxide (TiO₂), yttrium oxide (Y₂O₃), zirconium oxide (ZrO₂),indium oxide doped with tin (Sn), tin oxide doped with antimony (Sb),tin oxide doped with aluminum (Al). By the way, it is not preferable touse lead oxide, antimony oxide, and hafnium oxide from a viewpoint of ametallic element contained therein exerting adverse effects on theenvironment.

The diameter of such an oxide particle 1 is preferably larger than thatof the above-described fine gold particle 2, equal to or larger than 2.5nm and equal to or smaller than 80 nm. More preferably, it ranges from 5nm to 50 nm. When the diameter of the oxide particle 1 exceeds 80 nm, acolor filter or the like which is formed of the oxide compositeparticles looks whitish due to scattering of incident light, and whenthe particle diameter is equal to or larger than 50 nm, even if smallerthan 80 nm, the color filter or the like tends to look clouded.

Next, a method for producing the gold colloid/oxide composite particlehaving such a structure is explained taking a case of the oxide beingsilica (SiO₂) as an example.

First, a monodisperse gold colloid can be obtained by dropping atrisodium citrate solution into a boiled tetrachloroauric (III) acidsolution.

As shown in FIG. 2, since the equipotential point of the zeta potentialof the gold colloid is in the vicinity of pH 2, and the equipotentialpoint of silica being transparent oxide also ranges from pH 2 to pH 3,both gold colloid and silica are negatively charged in a solution havinga pH higher than 2. Therefore, the obtained gold colloid solution isdropped into a hydrophobic organic solvent, to which a cationicsurface-active agent or a nonionic surface-active agent has been added,to form a reverse micelle of gold colloid covered with thesurface-active agent.

Here, the cationic surface-active agents include alkylamine salt, alkyltrimethylammonium salt, dialkyl dimethylammonium salt, alkyldimethylbenzyl ammonium salt and the like, and the noionicsurface-active agents include polyoxyethylene alkyl phenyl ether,polyoxyethylene nonylphenyl ether, polyoxyethylene alkyl ether,polyoxyethylenepolyoxypropylene, polyoxyethyleneblockcopolymer,glycerine fatty acid ester, sorbitan fatty acid ester, sucrose fattyacid ester and the like. It is possible to use cyclohexane, toluene,benzene and the like as the organic solvent which is hydrophobic, thatis, insoluble in water.

Subsequently, ammonia solution is dropped as a catalyst into a reversemicelle solution having the gold fine colloids in an aqueous phase, andtetraethoxysilane (TEOS) is dropped thereinto, so that silanepolymerizes with the chain part of the surface-active agent on thesurface of the reverse micelles to produce silica, thereby obtaining adispersion of gold colloid/silica composite particles.

For production of a gold colloid/oxide composite particle with atransparent oxide other than silica as a matrix, it is possible to use,in place of tetraethoxysilane, alcoxides of the above-described metalssuch as titanium tetraethoxide and tin tetraethoxide, or complexes suchas acetate, acetylacetonates and the like.

Next, a second embodiment of the present invention is explained.

An oxide composite particle of the second embodiment has a structure, asshown in FIG. 3, in which at least one fine gold particle (gold colloid)2 is supported and fixed on the surface of an oxide particle 1.Hereinafter, the particle having such a structure is referred to as agold colloid/oxide support particle.

The diameter of the fine gold particle 2 preferably ranges from 2.5 nmto 35.0 nm. The particle diameter more preferably ranges from 10.0 nm to30.0 nm, and the most preferably from 10.0 nm to 25.0 nm.

As the oxide constituting the particle on which the fine gold particle 2is supported and fixed, an oxide transparent to visible light is used.Such possible transparent oxides include silica (SiO₂) aluminum oxide(Al₂O₃), cerium oxide (Ce₂O₃), indium oxide (In₂O₃), lanthanum oxide(La₂O₃), tin oxide (SnO₂), tantalum oxide (TaO_(x)), zinc oxide (ZnO₂),titanium oxide (TiO₂), yttrium oxide (Y₂O₃), zirconium oxide (ZrO₂),indium oxide doped with tin (Sn), tin oxide doped with antimony (Sb),tin oxide doped with aluminum (Al). By the way, it is not preferable touse lead oxide, antimony oxide, and hafnium oxide from a viewpoint of ametallic element contained therein exerting adverse effects on theenvironment.

The diameter of such an oxide particle 1 is preferably larger than thatof the above-described fine gold particle 2, equal to or larger than 2.5nm and equal to or smaller than 80 nm. More preferably, it ranges from 5nm to 50 nm. When the diameter of the oxide particle 1 exceeds 80 nm, acolor filter or the like which is formed of the oxide support particleslooks whitish due to scattering of incident light, and when the particlediameter is equal to or larger than 50 nm, even if smaller than 80 nm,the color filter or the like tends to look clouded.

Next, a method for producing the gold colloid/oxide support particlehaving such a structure is explained taking a case of the oxide beingsilica (SiO₂) as an example.

First, a hydrazine (N₂H₄) solution is dropped into 20 ml oftetrachloroauric (III) acid solution and agitated, and thereafter ahydrophobic organic solvent and a nonionic surface-active agent areadded thereto to obtain a dispersion of gold colloids. Further, anethanol solution of tetraethoxysilane (TEOS) is added to ammoniasolution, and thereafter solvent therein is evaporated forconcentration.

Next, the concentrated solution containing tetraethoxysilane (TEOS) isadded to the dispersion of gold colloids for reaction, the resultantmixed solution is sprayed into liquid nitrogen, followed by vacuumdrying, thereby obtaining gold colloid/oxide support particles.

Next, a third and a fourth embodiment of the present invention areexplained.

FIG. 4 is a cross-sectional view generally showing the structure of aphosphor with a surface coated with oxide composite particles, which isthe third embodiment of the present invention.

In this drawing, a numeral 3 denotes a phosphor particle that is a mainbody on which a coating film 4, which is composed of the above-describedgold colloid/silica composite particles according to the firstembodiment, is formed. Note that the coating film 4 may cover only apart of the surface of the phosphor particle 3. The coating film 4 maybe composed of the gold colloid/silica support particles according tothe second embodiment.

Here, as a phosphor constituting the phosphor particle 3, Y₂O₃:Eu,Y₂O₂S:Eu, (Y, Gd)BO₃:Eu, YBO₃:Eu and the like as having red luminescentcan be used. It should be noted that since a coating film having opticalcharacteristics other than red can be obtained by controlling theparticle diameter of the gold colloid, a usable phosphor is not limitedto red one.

The phosphor having such a coating film is produced by a methodexplained below. Specifically, an organic binder such as a polymer ofacrylic acid or styrene, gum arabic, gelatin, polyvinyl alcohol,polyethylene glycol, polyvinyl pyrrolidone, hydroxypropylcellulose orthe like, or an inorganic binder such as inorganic silicate, phosphate,aluminate or the like is added to a well-known phosphor suspension(slurry) so that a binder adheres to the surface of the phosphorparticle, thereafter a dispersion of the above-described goldcolloid/silica composite particles is added thereto and agitated, andthen the phosphor is taken out and dried, thereby obtaining a phosphorwith a surface covered with a thin film composed of the goldcolloid/silica composite particles.

Next, a color filter that is the fourth embodiment of the presentinvention is explained.

FIG. 5 is a cross-sectional view generally showing the structure of acolor filter of a cathode ray tube that is the fourth embodiment of theinvention.

In the drawing, a numeral 5 denotes a panel of a face plate, a lightabsorbing layer 6 a which is formed as a black matrix and a color filter6 b are arranged respectively on an inner surface of the panel 5, and aphosphor layer 7 of each color of blue, green, red is formed, arrangedin dots or stripes, on the color filter 6 b. In the color filter 6 b,each color filter layer is regularly arranged and formed in holes inpredetermined shapes (for example, in circular dots) of the lightabsorbing layer 6 a so as to transmit light of the same color as theluminous color of the phosphor layer 7. In this color filter 6 b, atleast a filter layer of one color is a thin film composed of theabove-described gold colloid/silica composite particles.

For production of such a filter layer, an organic binder such as apolymer of acrylic acid or styrene, gum arabic, gelatin, polyvinylalcohol, polyethylene glycol, polyvinyl pyrrolidone,hydroxypropylcellulose or the like, or an inorganic binder such asinorganic silicate, phosphate, aluminate or the like is first added toliquid made by concentrating the dispersion of the gold colloid/silicacomposite particles, which is obtained by the above-described method,thereby preparing a coating solution. Subsequently, a solvent havingvolatility characteristics suitable for its coating method is addedthereto to adjust its concentration, and thereafter applied onto asubstrate such as a face panel by a spin coating method, a dip coatingmethod, a screen printing method or the like and dried, thereby forminga filter layer of the color filter.

Further, patterning can be performed by a well-known photolithographymethod. Specifically, appropriately selected photosensitive componentsare added to the dispersion of the above-described gold colloid/silicacomposite particles to prepare a coating solution, which is applied to apanel, dried, and exposed and developed at a predetermined positionthrough a shadow mask, thereby forming a patterned filter layer.Alternatively, patterning can be performed by a bilayer photolithographymethod of individually laminating and forming photoresist coatings.

In the phosphor of the third embodiment and the color filter of thefourth embodiment formed as described above, a thin film is formed ofthe gold colloid/silica composite particles. In a thin film singlycomposed of the gold colloids, the particles aggregate together due todrying or grow to be black, but, in the thin film composed of the goldcolloid/silica composite particles, since the gold colloids aredispersed and contained in the matrixes of silica to exist independentlyfrom each other, the particle diameter is kept fine so that visiblelight is kept selectively absorbed in the surface plasmon absorption.

Next, a color cathode ray tube, a field emission display (FED), and aplasma display panel (PDP) are individually explained as examples ofcolor displays having such a phosphor coating film or a color filter.

The color cathode ray tube, as shown in FIG. 6A and FIG. 6Brespectively, has an envelope which includes a glass panel 5 that is atranslucent panel, a funnel 8, and a neck 9. A phosphor screen 10 isprovided on the inner surface of the panel 5, and a shadow mask 11 isdisposed inside the phosphor screen 10 to be opposed thereto. Inside theneck 9 of the envelope, an electron gun 13 is disposed which emitselectron beams 12. Further, inside the funnel 8, an inner shield 14 isdisposed which shields the electron beams 12 emitted from the electrongun 13 from an external magnetic field, and outside the funnel 8, adeflector 15 is disposed which deflects the electron beams 12 by amagnetic field generated thereby. The phosphor screen 10 comprises alight absorbing layer 16 formed in a matrix and phosphor layers 17 ofrespective colors, which are regularly arranged and formed in holes ofthe light absorbing layer 16, and a color filter 19 having filter layers18 of colors corresponding to those of luminous color of the phosphorlayers 17 is provided between the phosphor layers 17 and the panel 5.

In the field emission display (FED) that is a second example of thecolor display of the present invention, as shown in FIG. 7, a substrate20 on the side of emitting electrons and a substrate 21 on the side ofemitting light are disposed to be opposed to each other in parallel toform a vacuum envelope 22. In the substrate 20 on the electron emittingside, a silicon dioxide film 25 having many cavities 24 is formed on asilicon substrate 23, a gate electrode 26, which is made of molybdenum,niobium or the like, is formed thereon, and electron emitting elements27, which are made of molybdenum, in cone shape are formed on thesilicon substrate 23 inside the cavities 24. In the substrate 21 on thelight emitting side, a phosphor screen 10, which comprises a lightabsorbing layer and phosphor layers of respective colors, is formed on aface opposed to the electron emitting elements 27 of a glass panel 28,and a color filter (not shown) corresponding to luminous colors of thephosphor layers is provided between the phosphor layers and the glasspanel 28. Further, to support a load exerted on the silicon substrate 23by the weight of the glass panel 28 and the like and the atmosphericpressure, a supporting member 29 is disposed between the substrate 20 onthe electron emitting side and the substrate 21 on the light emittingside.

In the AC-type PDP that is a third example of the color display of thepresent invention, as shown in FIG. 8, a rear substrate 30 and a frontsubstrate 31 are arranged to be opposed to each other in parallel, andboth are held with a fixed gap interposed therebetween by a plurality ofcell barriers 32 which are arranged on a rear side glass substrate 30 a.In the front substrate 31, a light absorbing layer 16 and a color filter19 are arranged on an inner surface of a front side glass substrate 31a, and composite electrodes 35 are formed thereon, each composed of atransparent electrode 33 being a sustain electrode and a metal electrode34 being a bus electrode. Further, a dielectric layer 36 is formedcovering the composite electrodes 35, and a protective layer 37 isformed thereon. On a front face of the rear side glass substrate 30 a,address electrodes 38 are formed to be located between the cell barriers32 in a manner to be perpendicular to the composite electrodes 35, andphosphor layers 17 are provided in a manner to cover the addresselectrodes 38.

Next, characteristics of the thin film composed of the goldcolloid/silica composite particles, which is used as the coating film ofthe phosphor or the filter layer of the color filter in theabove-described embodiments, are explained according to FIG. 9.

First, the light transmittance spectrum of the aforesaid thin film wasmeasured with the diameter of the gold particle (colloid) changed toobtain the bottom wavelength of this spectrum (the wavelength having themaximum absorption rate). The relationship between the diameter of thegold colloid and the optical characteristics (the wavelength having themaximum absorption) of the thin film composed of the gold colloid/silicacomposite particles is shown in FIG. 9.

It was confirmed, as in this graph, that when the diameter of the goldcolloid is smaller than 2.5 nm, the bottom wavelength (the wavelengthhaving the maximum absorption) is on the side of significantly shortwavelength, and thus the thin film becomes yellowish and insufficient incoloring ability. It was also confirmed that when the diameter of thegold colloid is larger than 2.5 nm, the thin film becomes reddish (pink)in color, and that as the particle diameter becomes larger, the bottomwavelength shifts toward a long wavelength side so that the color of theobtained thin film becomes bluish purple. When the diameter of the goldcolloid exceeds 50 nm, the thin film becomes brown, and it becomes blackwhen the particle grows to be larger in diameter than the above.

Next, the results of measuring chromaticity characteristics of redluminescence with the diameter of the gold colloid changed in the colordisplay having a color filter layer composed of such gold colloid/silicacomposite particles, are shown in FIG. 10 together with characteristicsof a red filter layer which is formed using red iron oxide that is aconventional red pigment.

As in the chromaticity diagram shown in FIG. 10, it was confirmed thatas the diameter of the gold colloid is increased, the y value ofluminous chromaticity decreases and the x value thereof increases whenthe particle diameter is equal to or smaller than 25.0 nm, whichindicates improved chromaticity characteristics of red. It wasconfirmed, however, that when the particle diameter of the gold colloidis further increased beyond 25.0 nm, the y value of the chromaticityconversely increases and the x value decreases, which indicatesdeterioration in chromaticity characteristics.

From the measured results shown in FIG. 9 and FIG. 10, it is found thatthe particle diameter of the gold colloid preferably ranges from 2.5 nmto 35.0 nm, more preferably from 10.0 nm to 30.0 nm, and the mostpreferably from 10.0 nm to 25.0 nm. In other words, it is found from thegraph in FIG. 9 that the obtained thin film has an effect of coloring,in which the particle diameter of the gold colloid usable as a colorfilter ranges from 2.5 nm to 35.0 nm, and especially when the particlediameter of the gold colloid ranges from 10.0 nm to 30.0 nm, the thinfilm is usable as a red filter. Further, it is found from the graphshown in FIG. 10 that the particle diameter of the gold colloid, whichhas an effect of improving chromaticity characteristics of redluminescence, ranges from 10.0 nm to 25.0 nm.

Furthermore, the transmittance spectrum of the thin film composed ofsuch gold colloid/silica composite particles is shown in FIG. 11together with the transmittance spectrum of the filter layer formed ofred iron oxide. From this drawing, it was confirmed that thetransmittance of light within the ultraviolet wavelength region of thethin film composed of the gold colloid/silica composite particlesincreases to be about five times that of the filter layer composed ofred iron oxide, which indicates that the former thin film substantiallydecreases in absorption of light within the ultraviolet wavelengthregion as compared to the filter layer composed of red iron oxide.

To clarify such an effect, the irradiance (light exposure) of aphotoresist with ultraviolet rays required in a phosphor layer formingstep when the thin film composed of red iron oxide and the thin filmcomposed of the gold colloid/silica composite particles are respectivelyused as a phosphor coating film or a color filter of a color display,are shown in Table 1.

TABLE 1 Phosphor coating Color filter Red iron Gold Red iron Gold oxidecolloid oxide colloid coating Coating thin film thin film Required 100%60% 100% 80% exposure

It was confirmed, as in Table 1, that the use of the thin film composedof the gold colloid/silica composite particles decreases the lightexposure required by the photoresist in forming the phosphor layer forboth the phosphor coating film and the color filter, resulting inimproved productivity in an exposure step.

It should be noted that the oxide composite particle according to thepresent invention is suitable for a red phosphor coating film or a redfilter. In addition, composite particles having optical characteristicsother than red can be obtained since the bottom wavelength of the lighttransmittance spectrum is changed by controlling the particle diameterof the gold colloid, the molar ratio of the gold colloid to an oxide, orthe dielectric constant of the oxide. Therefore, it is possible toobtain phosphor coating films or color filters having various opticalcharacteristics from yellow to bluish green.

Specific embodied examples in which the present invention is applied todisplays are explained.

EXAMPLE 1

In the following procedure, a dispersion of composite particles (goldcolloid/silica composite particles) in which gold colloids are containedin matrixes of silica particles was prepared, and this dispersion wasused to produce a phosphor with a surface formed with a thin filmcomposed of the gold colloid/silica composite particles.

Specifically, 100 ml of 4.8×10⁻⁴ M (mol/l) tetrachloroauric (III) acid(HAuCl₄) solution was put into a rounded-bottomed flask and boiled in anoil bath by increasing its temperature to 100° C., and thereafter 1 mlof 2.8×10⁻⁵ M trisodium citrate dihydrate was dropped thereinto. Afterabout one minute and thirty seconds elapsed after the dropping, thesolution changed in color to red, which indicated that gold colloidswere produced. Subsequently, the rounded-bottomed flask was moved to acold-water bath to be rapidly cooled. The gold colloid dispersion thusobtained was concentrated by an evaporator into a total volume of 10 ml,to which 10 ml of cyclohexane and 4 ml of polyoxyethylene nonylphenylether as a nonionic surface-active agent were respectively added andquickly agitated for five minutes. Further, 7.6 ml of ammonia solutionwas dropped thereinto and agitated for five to ten minutes.Subsequently, 12 ml of 10% tetraethoxysilane (TEOS)/cyclohexane solutionwas slowly dropped into the obtained mixture and agitated for 12 hours,and then concentrated by the evaporator, thereby obtaining a dispersionhaving a high concentration of gold colloid/silica composite particles.

The molar ratio of the gold colloid/silica in the gold colloid/silicacomposite particle was 2.6% and the particle diameter of the goldcolloid was about 8 nm and the particle diameter of silica was about 30nm. The composite particle was colored in red.

Next, a red phosphor (Y₂O₂S:Eu) with a surface processed by aluminatewas mixed into the obtained dispersion of the gold colloid/silicacomposite particles and agitated, and thereafter the phosphor was takenout and dried, thereby obtaining a red phosphor with a surface coveredwith a thin film composed of the gold colloid/silica compositeparticles.

Moreover, using this phosphor, a color cathode ray tube was manufacturedin the conventional method. Specifically, a face panel, which had beenformed with a black matrix (BM) in advance, was prepared, and a bluephosphor (ZnS:Ag, Al), a green phosphor (ZnS:Cu, Al) and the redphosphor covered with the thin film composed of the above-described goldcolloid/silica composite particles were individually mixed into watertogether with PVA, ADC and a surface-active agent and agitated toprepare phosphor slurries of respective colors. Thereafter, the phosphorslurries of the respective colors were applied on the BM of the panel insequence and dried, and then exposed and developed at predeterminedpositions through shadow masks to form phosphor layers of the respectivecolors. Subsequently, a metal back layer was formed on thus formedphosphor layers, and then a funnel was sealed thereto, an electron gunwas installed therein and further the inside of the obtained tube wasexhausted to complete a color cathode ray tube.

Further, as Comparative Example 1, a red phosphor with a surface coatedwith red iron oxide was used to manufacture a color cathode ray tube inthe similar manner.

Chromaticity characteristics of red luminescence, and displaycharacteristics of brightness and contrast of the color cathode raytubes thus obtained in Example 1 and Comparative Example 1 respectively,were measured. The measured results are shown in Table 2.

EXAMPLE 2

In the following procedure, composite particles in which gold colloidsare supported and fixed on the surface of silica particles (goldcolloid/silica support particles) were produced, and the resultantparticles were used to produce a phosphor with a surface formed with athin film composed of the gold colloid/silica support particles.

Specifically, 0.05 ml of 1 M of hydrazine (N₂H₄) solution was droppedinto 20 ml of 8×10⁻⁴ M tetrachloroauric (III) acid (HAuCl₄) solution andagitated. The obtained solution changed in color to bluish purple, whichindicated that gold colloids were produced. Subsequently, 50 ml ofisooctane and 5 ml of a nonionic surface-active agent (Ingepal C-52)were individually added to this solution and agitated to obtain a firstsolution.

On the other hand, 4.36 g of 28% ammonia solution and 26 ml of purewater were mixed and added to 150 ml of ethanol. To this solution, asolution obtained by adding 8.33 g of TEOS to 50 ml of ethanol wasslowly added with agitation. Subsequently, the ethanol that is a solventof this solution was evaporated by the evaporator to be concentratedinto a total volume of 50 ml, thereby obtaining a second solution.

Next, the second solution was slowly added to the first solution withagitation and kept agitated for 24 hours. The mixed solution thusobtained was sprayed into liquid nitrogen in a Dewar vessel, andthereafter poured to a stainless tray and held in a vacuum constanttemperature bath at 200° C. for 24 hours for vacuum drying. The powderthus obtained was pink fine particles having a particle diameter of theorder of several microns. The particle was composed of compositeparticles having a particle diameter of the order of nanometers whichgathered to form porous aggregated spheres and could easily be crushedin a mortar.

Subsequently, a red phosphor (Y₂O₂S:Eu) with a surface processed byaluminate was mixed into a dispersion of the gold colloid/silica supportparticles thus obtained, and the phosphor was taken out after agitationand dried, thereby obtaining a red phosphor with a surface covered witha thin film composed of the gold colloid/silica support particles.Further, using this phosphor, a color cathode ray tube was manufacturedsimilarly to Example 1. Chromaticity characteristics of red luminescenceand display characteristics of brightness and contrast of the colorcathode ray tube thus obtained in Example 2, were measured respectively.The measured results are shown in Table 2.

TABLE 2 Comparative Example 1 Example 2 Example 1 Color cathode ray tubeBrightness 100 100 100 Red luminescence x value 0.641 0.641 0.640 yvalue 0.336 0.336 0.345 Contrast 103 103 100

EXAMPLE 3

The red phosphor with a surface covered with the gold colloid/silicacomposite particles produced in Example 1 was used to manufacture afield emission display (FED) as described below. Specifically, on a faceplate (glass panel), which had been formed with a BM in advance, a bluephosphor layer, a green phosphor layer and a layer of a red phosphorcovered with gold colloid/silica composite particles were formedsimilarly to Example 1 by patterning at respective predeterminedpositions, on which a metal back layer was formed. Then, the face platewas sealed to a rear substrate (rear plate) on which electron emittingelements had been formed in advance and the inside thereof was exhaustedto complete an FED. Further, as Comparative Example 2, a red phosphorwith a surface coated with red iron oxide was used to manufacture an FEDin the similar manner.

Chromaticity characteristics of red luminescence, and displaycharacteristics of brightness and contrast of the FEDs thus obtained inExample 3 and Comparative Example 2 respectively, were measured. Themeasured results are shown in Table 3.

EXAMPLE 4

The red phosphor with a surface covered with the gold colloid/silicacomposite particles produced in Example 1 was used to manufacture aplasma display as described below. Specifically, a blue phosphor, agreen phosphor and the red phosphor covered with the gold colloid/silicacomposite particles were individually mixed with terpineol and ethylcellulose and agitated to prepare phosphor pastes. These phosphor pasteswere coated by screen printing at respective predetermined positions ofa glass substrate, on which cell barriers had been formed, therebyobtaining a rear substrate having a phosphor pattern. Subsequently, thisrear substrate was fabricated with a front substrate, on which a BM, acomposite electrode, a dielectric layer and a protective layer had beenformed to complete a plasma display. Further, as Comparative Example 3,a red phosphor with a surface coated with red iron oxide was used tomanufacture a plasma display in the similar manner.

Chromaticity characteristics of red luminescence, and displaycharacteristics of brightness and contrast of the plasma displays thusobtained in Example 4 and Comparative Example 3 respectively, weremeasured. The measured results are shown in Table 3.

TABLE 3 Comparative Comparative Example 3 Example 2 Example 4 Example 3Field emission display Plasma display Brightness 100 100 100 100 Redluminescence x value 0.642 0.640 0.633 0.631 y value 0.334 0.344 0.3410.352 Contrast 102 100 101 100

It is found from Table 2 and Table 3 that Examples 1, 2, 3 and 4 improvein contrast as compared to corresponding Comparative Examples 1, 2 and3, and remarkably improve in chromaticity of red luminescence.

EXAMPLE 5

An appropriately selected sensitizer was added to the dispersion of thegold colloid/silica composite particles used in Example 1 to prepare ared filter coating solution. Then this red filter coating solution and ablue filter coating solution containing a blue pigment (for example,cobalt aluminate (Al₂O₃—CoO)) and a green filter coating solutioncontaining a green pigment (for example, TiO₂—NiO—CoO—ZnO) which hadbeen prepared by a well-known method were used respectively andpatterned by a well-known photolithography method to form a color filteron a face panel with a BM.

Thereafter, similarly to Example 1, phosphor layers and a metal backlayer were formed in sequence, a funnel was sealed thereto, an electrongun was installed therein, and then the inside of the obtained tube wasexhausted to complete a color cathode ray tube including a color filter.It should be noted that the thin film composed of the goldcolloid/silica composite particles remained red without turning to blackeven by heat treatments in sealing and exhausting steps. Further, asComparative Example 4, a red filter layer was formed using red ironoxide that is a conventional red pigment to manufacture a color cathoderay tube including a color filter in the similar manner.

Chromaticity characteristics of red luminescence, and displaycharacteristics of brightness and contrast of the color cathode raytubes thus obtained in Example 5 and Comparative Example 4 respectively,were measured. The measured results are shown in Table 4.

EXAMPLE 6

Using the red filter coating solution, the blue filter coating solutionand the green filter coating solution, which are used in Example 5,respectively, filter patterns were formed on a face plate (glass panel)similarly to Example 5, and the resultant panel was used to manufacturea field emission display (FED) including a color filter similarly toExample 3. Further, as Comparative Example 5, a red filter layer wasformed using red iron oxide that is a conventional red pigment, and anFED including a color filter was manufactured in the similar manner.

Chromaticity characteristics of red luminescence, and displaycharacteristics of brightness and contrast of the FEDs thus obtained inExample 6 and Comparative Example 5 respectively, were measured. Themeasured results are shown in Table 4.

EXAMPLE 7

Using the red filter coating solution, the blue filter coating solutionand the green filter coating solution, which are used in Example 5,respectively, filter patterns were formed on an inner surface of a glasssubstrate on the front side similarly to Example 5, and the resultantsubstrate was used as a front substrate to manufacture a plasma displayincluding a color filter similarly to Example 4. Further, as ComparativeExample 6, a red filter layer was formed using red iron oxide that is aconventional red pigment, and a plasma display including a color filterwas manufactured in the similar manner.

Chromaticity characteristics of red luminescence, and displaycharacteristics of brightness and contrast of the plasma displays thusobtained in Example 7 and Comparative Example 6 respectively, weremeasured. The measured results are shown in Table 4.

TABLE 4 Comparative Comparative Comparative Example 5 Example 4 Example6 Example 5 Example 7 Example 6 Color cathode Field emission Plasma raytube display display Brightness 100 100 100 100 100 100 Red luminescencex value 0.651 0.650 0.651 0.649 0.642 0.640 y value 0.336 0.345 0.3360.344 0.344 0.353 Contrast 103 100 104 100 101 100

It is found from Table 4 that Example 5, 6 and 7 improve in contrast ascompared to corresponding Comparative Examples 4, 5 and 6, andremarkably improve in chromaticity of red luminescence.

INDUSTRIAL APPLICABILITY

As has been described, the gold colloid/silica composite particle of thepresent invention contains no toxic substance that causes anenvironmental problem and is excellent in optical characteristics andheat resistance, so that a phosphor or a color filter which is excellentin optical characteristics, heat resistance and non-toxicity can beobtained. Further, a color display can be obtained which includes such aphosphor or color filter and is excellent in luminous chromaticitycharacteristics and display characteristics of brightness and contrast.Therefore, the gold colloid/silica composite particle of the inventionhas extremely great industrial value.

1. A method for producing coated phosphor particles, comprising: preparing an aqueous dispersion containing fine gold particles; adding a surface-active agent and a hydrophobic organic solvent to the aqueous dispersion of the fine gold particles obtained in the previous step to form reverse micelles of the fine gold particles; adding tetraethoxysilane to the reverse micelles of the fine gold particles, wherein polymerization is carried out to produce a dispersion comprising gold colloid/oxide composite particles; adding an organic or inorganic binder to a suspension of phosphor particles to allow the binder to adhere to surfaces of the phosphor particles; and thereafter adding the dispersion containing the gold colloid/oxide composite particles thereto, and mixing followed by drying to form a thin film containing the gold colloid/oxide composite particles on at least part of the surface of each of the phosphor particles.
 2. A color display, comprising: a panel having a light transmission property; a light absorbing layer disposed on an inner surface of the panel; and a phosphor layer disposed on a rear side opposite to the panel with respect to the light absorbing layer, the phosphor layer comprising the coated phosphor particles produced according to claim
 1. 3. The method according to claim 1, wherein the surface-active agent is a cationic or nonionic surface-active agent.
 4. The method according to claim 3, wherein ammonia solution is added to catalyze said polymerization.
 5. A color display, comprising: a panel having a light transmission property; a light absorbing layer disposed on an inner surface of the panel; and a phosphor layer disposed on a rear side opposite to the panel with respect to the light absorbing layer, the phosphor layer comprising the coated phosphor particles produced according to claim
 3. 6. A method for producing coated phosphor particles, comprising: preparing an aqueous dispersion containing fine gold particles; adding a surface-active agent and a hydrophobic organic solvent to the aqueous dispersion of the fine gold particles obtained in the previous step to form reverse micelles of the fine gold particles; adding at least one compound selected from the group consisting of alcoxides, acetates, and complexes of titanium or tin to the reverse micelles of the fine gold particles, wherein polymerization is carded out to produce a dispersion comprising gold colloid/oxide composite particles; adding an organic or inorganic binder to a suspension of phosphor particles to allow the binder to adhere to surfaces of the phosphor particles; and thereafter adding the dispersion containing the gold colloid/oxide composite particles thereto, and mixing followed by drying to form a thin film containing the gold colloid/oxide composite particles on at least part of the surface of each of the phosphor particles.
 7. The method for producing coated phosphor particles as set forth in claim 1, wherein the at least one compound is titanium tetraethoxide or tin tetraethoxide.
 8. A color display, comprising: a panel having a light transmission property; a light absorbing layer disposed on an inner surface of the panel; and a phosphor layer disposed on a rear side opposite to the panel with respect to the light absorbing layer, the phosphor layer comprising the coated phosphor particles produced according to claim
 6. 9. The method according to claim 6, wherein the surface-active agent is a cationic or nonionic surface-active agent.
 10. The method according to claim 9, wherein ammonia solution is added to catalyze said polymerization.
 11. A color display, comprising: a panel having a light transmission property; a light absorbing layer disposed on an inner surface of the panel; and a phosphor layer disposed on a rear side opposite to the panel with respect to the light absorbing layer, the phosphor layer comprising the coated phosphor particles produced according to claim
 9. 